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Book Chapter

Short-Term Sea-Level Changes and Coastal Erosion

By
PAUL D. KOMAR
PAUL D. KOMAR
College of Oceanography, Oregon State University, Corvallis, Oregon 97331
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DAVID B. ENFIELD
DAVID B. ENFIELD
College of Oceanography, Oregon State University, Corvallis, Oregon 97331
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Published:
January 01, 1987

Abstract:

Investigations of the role of sea level in producing coastal erosion have focused mainly on the long-term rise due to melting of glaciers and thermal expansion of sea water. There are, however, additional shorter term changes in the local sea level produced by a variety of ocean processes. Variations in the coastal currents, for example, can alter the water level at the shoreline due to the geostrophic balance between the current and the offshore sea-surface slope. Other factors which may alter local sea level include changes in atmospheric pressure, winds blowing either in the longshore or cross-shore directions, and the occurrence of upwelling. Because the inclined continental shelf and slope act as a wave guide, the fluctuations often become trapped and propagate over longshore distances beyond where they are actually generated. In that many of these processes are typically seasonal, the responding sea level also has a pronounced seasonal cycle, but frequently there can be significant fluctuations at periodicities of several days to a few weeks. The magnitudes of such changes vary considerably with coastal location but are typically on the order of 10 to 30 cm, achieving a maximum of about 100 cm in the Bay of Bengal.

The occurrence of an El Niño in the equatorial Pacific is known to have considerable impact on the erosion of the coasts of California and Oregon. This occurs because associated with an El Niño are shifts in the storm paths and a temporary rise in sea level. An El Niño is a breakdown of the normal equatorial wind and current patterns. This breakdown releases water which is normally set up in the western Pacific by the trade winds. The release creates a “wave” of sea-level rise, which first propagates eastward along the equator and then poleward along the eastern ocean margin. Such “waves” have been measured in the tide records of the western United States, amounting to some 20 to 60 cm and lasting for several months. Such transient sea-level changes have likely played an important role in coastal erosion.

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SEPM Special Publication

Sea-Level Fluctuation and Coastal Evolution

Dag Nummedal
Dag Nummedal
Department of Geology and Geophysics Louisiana State University, Baton Rouge, Louisiana
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Orrin H. Pilkey
Orrin H. Pilkey
Department of Geology Duke University, Durham, North Carolina
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James D. Howard
James D. Howard
Skidaway Institute of Oceanography Savannah, Georgia
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SEPM Society for Sedimentary Geology
Volume
41
ISBN electronic:
9781565760950
Publication date:
January 01, 1987

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